Fix PHP Scoper Problems

[jakejackson1]

Description

In older versions of WordPress without the str_starts_with() or str_ends_with() polyfills, a fatal error could occur in Mpdf when using a PHP version less than 8.0.

Testing instructions

1. Install WordPress 5.8
2. Run PHP7.4
3. Generate a PDF

Prior to this patch a PHP error would occur. After this patch, the PDF generates without issue.

Screenshots

Checklist:

• [x] I've tested the code.
• [ ] My code is easy to read, follow, and understand
• [ ] My code follows the accessibility standards.
• [ ] My code has proper inline documentation / docblocks.

Additional Comments

[codecov[bot]]

Codecov Report

Attention: 2 lines in your changes are missing coverage. Please review.

Comparison is base (3bd2e7d) 75.13% compared to head (0f23494) 75.13%.

Files	Patch %	Lines
src/autoload.php	0.00%	2 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## development #1487 +/- ## ================================================= - Coverage 75.13% 75.13% -0.01% Complexity 2953 2953 ================================================= Files 243 243 Lines 12882 12883 +1 Branches 370 370 ================================================= Hits 9679 9679 - Misses 3195 3196 +1 Partials 8 8 ```

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